DESCRIPTION: This is an epidemiologic study that will investigate the relationship between workplace exposure to boron containing compounds (including boric acid, borax) and adverse male reproductive effects. Boric acid has been identified as one of the highest priority chemicals for human field study by Moorman et al. (2000) in their review of 43 National Toxicology Program reproductive toxicants. Prioritization was based on the strength of animal data, estimated numbers of humans exposed in the workplace, and lack of adequate reproductive health effects data for the human. Animal studies show boric acid has effects on male reproduction at comparatively lower doses than other known reproductive toxicants, reproductive system sensitivity over other toxicities, and a probable threshold for adverse effects. Three human studies have published results on reproductive effects of occupational boron exposure. Two found no effect on fertility or development and one found testicular atrophy and sterility. All three have been criticized for study design issues or lack of adequate exposure assessment. A need still exists for a definitive human reproductive study. Therefore, the specific aims of this research are to: (1) Describe the relationship between boron exposure and direct measures of toxicity on male reproduction: total sperm count, sperm density, viability, motility, morphology, and sperm X:Y chromosome ratios sperm chromatin integrity measured by sperm chromatin structure assay (SCSA), COMET, TUNEL, protamine 1 (P1), protamines 2-4 (HP2-4), and protamine 2 precursor proteins (HPI1-2, HPS1-2) in ejaculated sperm cells; blood and urine steroid hormone markers including testosterone, free testosterone, serum hormone binding globulin, dihydrotestosterone, LH, FSH, estrone, estradiol, estriol; (2) describe the relationship between boron exposure and indirect measures of toxicity on male reproduction: fertility history and physical exam data; and (3) describe the relationship between workplace, environmental, and dietary sources of boron with biomarkers of exposure and reproductive effect. The goal is to contribute critical information on the exposure level at which boron causes adverse effects on human male reproduction. The information could then be used to inform workplace practices and policies to protect the reproductive health of the hundreds of thousands of men estimated to be exposed to boric acid and other boron containing compounds in the workplace.